In the search for better protection from environmental contamination, study of indicator systems demonstrating high sensitivity is particularly valuable. One such system is eggshell formation in several raptorial and piscevorous birds. Production of thin shelled, easily broken eggs by these birds provided one of the earliest indications that environmental contaminants, in this case DDT and/or its metabolites such as DDE, could have severe ecological and human health impact. The mechanism underlying DDT-induced inhibition of shell gland function is still not understood. Another possible indicator system involves young seabirds such as shearwaters, puffins, and petrels which are currently dying in large numbers on both sides of the Atlantic from an unknown cause. We suspect osmoregulatory failure in these totally marine birds resulting from inhibition of nasal salt gland function by organochlorines such as DDT and PCB's which are still accumulating in the sea. The proposed research would evaluate with both in vivo feeding and in vitro dose-response experiments the roles of carbonic anhydrase and the several ion-transport ATPases in organochlorine induced eggshell thinning and possible osmoregulatory failure. These enzymes appear to be inhibited by organochlorines in many animal tissues and are known to be present in avian shell and salt glands. Initial work would utilize the readily available domestic duck in which we have demonstrated to date: DDE-induced thinning, a shell gland Ca ion-ATPase, and some DDE-inhibition of both plasma osmoregulation and nasal gland Na ion, K ion-ATPase. Field work in the Mount Desert Island region would be undertaken to verify findings in appropriate wild species, e.g., herring gull, double-crested cormorant, guillemot, and Leach's petrel. The significance of the proposed work is that full mechanistic understanding of important indicator systems is necessary for maximal effectiveness in assessing the health impact of potential contaminants.